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Like most people, we’re using git right at the centre of our puppet config management workflow. As I’ve mentioned previously, it features prominently in my top 10 most frequently used commands.

Our workflow is based around feature branches, and quite often we end up in a situation where we have a lot of local branches which have already been merged in the copy held upstream on github/gitlab/etc.

Today, I looked and noticed that while we only had 4 active branches on the gitlab server I had 41 branches locally, most of which related to features fixed a long time ago.

This doesn’t cause much of a problem although it can get confusing (especially if you’re likely to re-use a branch name in the future) – 41 branches is enough that deleting them one at a time by hand is tedious.

It looks like some gui tools/IDEs will take care of this for you, but I’m a command line kinda guy, and the git command line tools don’t seem to quite have this functionality baked in.

After a bit of poking about, I came up with the following approach which deletes any branch which no longer exists upstream.

Making this work with create_resources and trying to splice in the the username for each user in the list into a hash looked like it would be messy, requiring at least an additional layer of define — this method is much neater.

This makes it much easier to create data abstractions over existing modules — you can programmatically massage the data you read from your hiera files and call definitions using that data in a much more flexible way than when passing hashes to create_resources. This “glue” can be separated into your roles and profiles (which could be the subject of another post but are described well in this blog post), creating a layer which separates the use of the module from the data which drives that use nicely.

So this all sounds pretty great, but there are a few changes you’ll possibly encounter when switching to the future parser:

Similar to the switch from puppet master to puppet server, the future parser is somewhat more strict about data formats. e.g. I found that my hiera data definitely needed to be properly quoted when I started using puppet server, so entries like mode : 644 in a file hash wouldn’t give the number you were expecting… (needs mode : 0644 or mode : '644' to avoid conversion from octal to decimal…). The future parser extends this to being more strict in your manifests, so a similarly-incorrect file { ... mode => 644 } declaration needs quoting or a leading zero. If you use puppet-lint you’ll catch this anyway — so use it! 🙂

It’s necessary to use {} instead of undef when setting default values for hiera_hash (and likewise [] instead of undef for hiera_array), to allow conditional expressions of the form if $var { ... } to work as intended. It seems that in terms of falseness for arrays and hashes that undef is in fact true… (could be a bug, as this page in the docs says: “When used as a boolean, undef is false”)

Dynamically-scoped variables (which are pretty mad and difficult to follow anyway, which is why most languages avoid them like the plague…) don’t pass between a class and any sub-classes which it creates. This is in the docs here, but it’s such a common pattern that it could well have made it through from your old (pre-Puppet 2.7) manifests and still have been working OK until the switch to the future parser. e.g.:

Instead you need to explicitly qualify your variables to pull them out of the correct scope — $foo::var in this case. In your erb templates, as a common place where the dynamically-scoped variables might have ended up getting used, you can now use scope['::foo::var'] as a shorthand for the previously-longer scope.lookupvar('::foo::var') to explicitly qualify the lookup of variables. The actual scope rules for Puppet < 2.7 are somewhat more complicated and often led to confusing situations if you unintentionally used dynamic scoping, especially when combined with overriding variables from the parent scope…

I’m not sure that expressions of the form if "foo" in $arrayvar { ... } work how they should, but I’ve not had a chance to investigate this properly yet.

Most of these are technically the parser more strictly adhering to the specifications, but it’s easy to have accidentally had them creep into your manifests if you’re not being good and using puppet-lint and other tools to check them.

In conclusion : Start using the Future Parser soon! It adds excellent features for iteration which make abstracting data a whole lot easier than using the non-future (past?) parser allows. Suddenly the combination of roles, profiles and the iteration facilities in the future parser mean that abstraction using Puppet and hiera makes an awful lot more sense!

The majority of the servers I look after are managed by puppet[1], but we have a suite of 10 older servers which fall outside of that management environment.

We’re slowly replacing them with Shiny! New! Managed! Servers! ™ but until we’ve completed that work we’re stuck with limited management tools, doing things manually at the command line, like it’s still the 20th century[2]

Occasionally we need to do the same thing on every server (eg kick off a “yum update” or whatever) and using ssh to connect to them all one at a time is tedious.

So, we use cssh which is a scary… dangerous… “powerful” tool that spawns a load of ssh sessions and allows you to send the same keypresses to all the servers at once. I don’t like using it, it feels like a really dirty way to admin a bunch of hosts, but sometimes it’s a necessary evil.

As long as you’re careful what you type, and don’t do anything daft like “sudo bash” then you can keep a lid on the fear.

One of the “features” of this bundle of 10 servers is that they’re dual stack IPv4 and IPv6, but ssh is only accepting connections on the IPv4 address.

If you’re connecting to these one at a time, “ssh -4 server.name.bris.ac.uk” will sort that out for you, but it took a little more rummaging in man pages to come up with the cssh alternative, and that’s the real purpose of this post.

Todays Tip
To force cssh to use IPv4 when connecting to a bunch of hosts, use:

cssh --options="-o AddressFamily=inet" <host list>

[1] Other config management systems are available 🙂
[2] To be fair, sometimes it’s also useful to kick off a puppet run everywhere